This is a decimal value, extended to modify the other CVs when written. The
CVs to be modified and their new values are stored in two arrays for
simplicity.

The NMRA has decided that writing CV1 causes other CVs to update within the
decoder (CV19 for consisting, CV29 for short/long address). We want DP to
overwrite those _after_ writing CV1, so that the DP values are forced to be
the correct ones.